This invention relates to low-temperature fluid-bed chlorination of titaniferous ores using porous carbon reductants.
Titaniferous materials are often subjected to chlorination as chlorination is an efficient and economical way to obtain a high purity source of titanium for making titanium alloys, titanium compounds, and especially pigmentary titanium dioxide. Several processes have been described in the art for the chlorination of titaniferous materials. Such processes generally react a titanium-containing raw material such as rutile ore or ilmenite ore, with a chlorine-providing material and a carbon reductant according to one or both of the following equations: EQU TiO.sub.2 +2CL.sub.2 (g)+C(s).fwdarw.TiCl.sub.4 (g)+CO.sub.2 (g) EQU TiO.sub.2 +2CL.sub.2 (g)+2C(s).fwdarw.TiCl.sub.4 (g)+2CO(g)
Conventional chlorination reactions are generally carried out at about 1000.degree. C., but can be carried out at any temperature in the range from about 800.degree. C. to about 2000.degree. C., using various carbon reductants and chlorine sources.
Low-temperature chlorination, i.e. at a temperature below 800.degree. C., has also been suggested. U.S. Pat. No. 2,761,760 suggests chlorinating a titaniferous material at a temperature as low as 400.degree. C. using NOCl or a blend of NOCl and Cl.sub.2 as the chlorinating agent and preferably using a finely ground carbon reductant. The NOCl is described as being a very reactive chlorinating agent and the reactants are finely ground to increase their reactivity; however, substantially complete chlorination is not obtained. At best 78% of the Ti is chlorinated. U.S. Pat. No. 2,936,217 describes another chlorination process which operates at temperatures from 700.degree. C. to 950.degree. C. Finely ground carbon and finely ground titanium oxide material of controlled particle size are mixed and the mixture is agglomerated into granules of further controlled particle size. The granules are then fluidized and reacted with a chlorine source. However, it is taught that the carbon source is a relatively unimportant factor in this process and that only particle size is worthy of control. Further, it is taught that preagglomeration must be practiced here to achieve effective reaction.
Contrary to the teachings of the prior art, I have found that the carbon used in the low-temperature chlorination of a titaniferous material can have a substantial effect on the completeness of said chlorination reaction. Further, I have found that fluidized bed techniques can be effectively used in low-temperature clorination of granular titaniferous materials without the use of heretofore required fine grinding, preagglomeration of titaniferous material and carbon reductant, or resorting to highly reactive chlorine sources such as NOCl.
In accord with the present invention, I have found that titanium-containing materials and ores can be substantially chlorinated in a fluidized bed process at surprisingly low temperatures of about 600.degree. C. to about 800.degree. C. if a porous granular carbon is used as the carbon reductant.
It is therefore an object of the present invention to chlorinate titanium-containing materials and ores in a fluid bed at a temperature of between about 600.degree. C. and 800.degree. C. using a porous carbon reductant.
A further object and advantage of the present invention is that the present low-temperature chlorination process is more selective relative to impurity oxides in the materials and ores being chlorinated resulting in greater reactor efficiency and ease of operation due to the absence of normally liquid or sticky chlorides produced during high-temperature chlorination processes which adhere to reactor surfaces.
A still further object and advantage of the present chlorination process is that the fluidized bed is maintained in its fluidized condition with greater ease due to the lower temperatures and associated reduced softening and melting of fluidized materials.
These and other objects and advantages of the present invention will become more apparent from the detailed description of the invention.